Myocardial perfusion imaging (MPI) is the most common tool for non-invasively evaluating ischemia in patients with suspected coronary artery disease (CAD). This technique contributes substantially to the risk-stratification of CAD patients, in terms of their likelihood to encounter coronary events and cardiac death. Therefore, MPI provides valuable information which assists clinical decision-making with regard to medical treatment and intervention. There is a growing and consistent evidence that gated MPI provides additional clinically useful data towards patient risk stratification, by enabling the assessment and comparison of left ventricular function during both post-stress and rest conditions.
Current data suggest that positron emission tomography (PET) MPI is a powerful modality for diagnosing obstructive CAD, and appears to provide better diagnosis than single photon emission computed tomography (SPECT); this is primarily related to PET technological advantages, such as higher count sensitivity, better spatial resolution and more accurate attenuation correction. The ability to quantify myocardial perfusion in absolute values is an added advantage of PET over SPECT, particularly in multivessel CAD.
Despite the known advantages of PET, SPECT tracers and [99mTc]-MIBI, in particular, are more prevalent in clinical practice. This is primarily due to the two following reasons: (i) the use of SPECT radiopharmaceuticals is logistically easier, and tracer dose price is usually lower than the respective cyclotron-produced PET pharmaceuticals, and (ii) existing PET MPI probes have short physical half lives, which require in-house production, and more importantly, have sub-optimal pharmacokinetic profiles, which most likely withhold the shift of nuclear cardiology from SPECT to the superior PET modality.
Nevertheless, in light of the potential contribution of PET to the field of MPI, increasing efforts were invested into the development of new PET MPI probes.
In the last decade, a wealth of effort has been invested into the development of optimal PET myocardial perfusion agents. Several fluorine-18 labeled myocardial flow tracers were reported in the literature. [18F]RP1004 [1], [18F]FBnTP [2, 3] and [18F]FDHR [3] base their cardiac accumulation on interactions with mitochondria which are plentiful in the heart muscle. The longer half-life of fluorine-18 enables extensive radiochemical transformations, extended PET scan times and commercial distribution. A wait of a period of four to five half-lives is ideally required between equal doses administered at rest and stress tests to allow for radioactivity from the first injection to decay to a point where it does not interfere significantly with the later scan. Fluorine-18 based tracers may prevent performance of both scans during a single day or at least require several hours stay interval while using an initial low dose followed by a high dose later, similarly to a “one-day protocol” used with 99mTc-labled SPECT flow tracers.
Several publications discuss the utilization of radiolabled tracers in molecular imaging techniques such as PET.